1. Field of the Invention
The present invention relates generally to a complex antenna, and more particularly, to a complex antenna which corresponds to both a circularly polarized wave and a linearly polarized wave.
2. Description of the Related Art
Portable wireless devices which are capable of making communications using a satellite, such as Global Positioning Systems (GPS) phones and Personal Data Assistants (PDA), are increasingly popular and necessary. For example, there are safety advantages such as a user being able to immediately send exact position information obtained by using a GPS satellite to a police or fire station via a mobile phone base station in an emergency. In addition, satellite radio using a broadcasting satellite has good sound quality, many channels and a wide coverage area. Thus, a rapid proliferation of GPS or satellite radio is expected.
Antennas in which both ground communication and satellite communication are possible are needed in the above-described usages.
Since the GPS or satellite radio has circularly polarized waves, a patch antenna or a four-wire helical antenna is used therein. Since mobile phones or wireless Local Area Networks (LAN) have linearly polarized waves, a monopole antenna is used therein.
A technique of an antenna which corresponds to both a circularly polarized wave and a linearly polarized wave is disclosed in Japanese Patent Laid-open Publication No. 2002-314312. According to this disclosure, a monopole antenna is disposed in the vicinity of the center axis of a four-wire helical antenna and both of the antennas correspond to a circularly polarized wave and a linearly polarized wave. However, this combination causes a miniaturization effect, which is detrimental to the antenna performance.